The present invention relates generally to methods of controlling an irrigation system. More specifically, the-present invention relates to methods of controlling an irrigation system to minimize the amount of irrigation water applied to a turf or crop while still meeting the crop or turf,s water requirements. Still more specifically, the present invention relates to methods of controlling an irrigation system that minimizes water use by setting irrigation schedules to take maximum advantage of natural rainfall, soil response to watering on a historical basis and the maturity of the turf or crop""s root systems.
Normally, vegetation and greenery grow in soil watered by rain. Where rain is so seasonal that the quantity of rainfall fails to meet the requirements of particular types of vegetation, or when the amount of rainfall is deficient or practically nonexistent, the extreme drying of the soil may retard, and eventually prevent, vegetation growth. Irrigation can compensate for the vicissitudes of nature by supplying water directly to areas of vegetation and greenery in regular intervals and in sufficient volumes.
Earlier techniques and methods of irrigation which were utilized to provide supplemental watering to vegetation and greenery located remote distances from a water source, traditionally included, for example, such methods as supplying water manually by hand and bucket directly to the vegetation, or by such means as constructing simple aqueduct systems. Aqueduct systems of the prior art were generally constructed by forming long furrows or canals immediately alongside the vegetation or greenery to provide moisture and promote vegetation growth and productivity. Over time, various other types of irrigation techniques and devices were developed by those skilled in the art to simplify and supplement traditional methods of irrigation. For example, simple mechanical lifting aids and animal-powered irrigation devices were developed to assist users in transporting water from a water source to a localized area of vegetation requiring supplemental irrigation. The farmer, who used his skill and experience to determine when the flow of water should be started and stopped to yield a good crop, controlled these early devices.
As technology progressed with the advent of steam power, the internal combustion engine and electricity, irrigation systems became fully mechanized operations in many parts of the world. Many of the earlier traditional techniques and methods of providing irrigation were replaced by mechanical devices with internal programmable timer units. Moreover, mechanical irrigation devices of the prior art revolutionized the irrigation industry by providing a novel means for automating the control of water flow from a pressurized water source through such means, as for example, portable, lightweight aluminum piping, to numerous watering stations located remote distances from the water source.
Traditionally, automatic electromechanical controllers of the prior art incorporate multiple conventional motor-driven electric clocks which provide a mechanized means for programming individual start times for various irrigation cycles and watering stations. Calendar programs are generally incorporated to provide a means for selecting particular days of operational watering which normally includes a period over 14 days. Typically, calendar programs used in conjunction with prior art electromechanical controllers are functionally realized through the use of a disc being mechanically rotated to a next day position by a conventional motor-driven clock, once every 24 hours.
Employed in all but the simplest versions of electromechanical irrigation controllers of the prior art, cycle start circuits are typically provided to activate additional timer motors for advancing the irrigation controller through multiple preset watering cycles. Pins are generally placed in clock dials to close a switch at a preset time and, if the circuit is completed through a switch held closed by the calendar wheel pin on a day designated for irrigation, the watering cycle typically starts. In this regard, cycling water from station to station and programming watering intervals and timing durations for individual watering stations or zones may be accomplished by the placement and specific arrangement of various functional pins, cams, levers and other mechanical devices of prior art electromechanical controllers which interact with one another in concert to provide preprogramming automation for an irrigation system.
Increasing the number of watering zones or stations of prior art automatic electromechanical irrigation controllers to expand the watering capabilities of the irrigation system and provide water to larger areas of vegetation or greenery, such as golf courses, cemeteries, or parks, typically involves a significant number of mechanical disadvantages in the overall performance of the irrigation system. Moreover, in expansion of the watering capabilities of an irrigation system employing automatic electromechanical controllers of the prior art generally requires a dramatic increase in the number of working parts to realize and effectuate the additional programming capabilities typically required when increasing the number of watering stations or zones of an initial irrigation system.
In response to the problems associated with the dramatic increase in mechanical working parts required by prior art electromechanical irrigation controllers when expanding the watering capabilities of an irrigation system, those skilled in the art developed automatic solid state irrigation controllers which eliminated electric motors, mechanical switches, actuating pins, cams, levers, gears and other mechanical devices typically associated with electromechanical controllers and replaced them with solid state electronic circuitry. The programming potential of automatic solid state controllers of the prior art generally permits the user to program, for example, multiple start times and day programs for individual watering stations, repeat cycles, watering time selections in minutes (sometimes seconds), while maintaining the split-second accuracy of solid state timing without requiring the numerous interacting mechanical parts employed by prior art electromechanical irrigation controllers.
Automatic solid-state irrigation controllers of the prior art typically provide a user with several program sequences from which to select. Generally, the user has the option to choose from multiple program sequences offered by the controller and determine the specific program options which best accommodate the particular watering needs of the user""s vegetation and greenery in a most advantageous manner. In this regard, each of the various program sequences typically has independent start times that may include several start times per day. In all the prior art known to the present inventors, the start time of the watering event is specified. The system then delivers water for a set amount of time.
To accommodate and sustain multiple program sequences, solid state irrigation controllers of the prior art generally incorporate a programmable microprocessor-controlled user interface that provides a user with the capability of programming several sprinkling stations or zones in a variety of timing scenarios, for example, daily, weekly, odd days, even days, etc. Each watering station or zone usually includes one or more sprinklers and a solenoid valve that is generally regulated by the microprocessor unit. Solenoid valves typically control the flow of water entering a particular watering station from a pressurized water source, and provide a means for monitoring the flow of water exiting the watering station through various sprinkler lines that typically terminate into a plurality of sprinkler heads strategically located throughout an irrigation area.
Other general features of automatic solid-state irrigation controllers of the prior art may include manual modes of operation that generally function to provide the user with an option of overriding all preprogrammed automatic watering operations of an irrigation controller. For example, manual operational modes of prior art solid state irrigation controllers may be utilized when excessive amounts of rain have fallen, or when a lengthy spell of dry weather has occurred requiring greater quantities of irrigation than previously programmed by the user to sustain vegetation growth and productivity.
Manual override functions on irrigation systems are being automated as water becomes more expensive. A rain sensor is a simple device, usually employing a wetable disk that activates an electrical circuit when dampened by rain, which is mounted in an open area outdoors and wired to the shutoff valve on the common line of the irrigation system. Rain sensors are designed to override the cycle of an automatic irritation system when adequate rainfall has been received. They are simple xe2x80x9conxe2x80x9d or xe2x80x9coffxe2x80x9d sensors. Rain sensors are now being made mandatory. For example, Ordinance 1948, which was adopted on Aug. 14, 1997 by the town of Cary, N.C., requires a rain sensor to be installed on all new and existing commercial irrigation systems and set to turn off the irrigation system when xc2xcxe2x80x3 of rainfall has occurred.
Large-scale central control of irrigation can be economically important. For example, the San Diego Unified School District is installing a Rain Bird computerized Maxicom2 Central irrigation control system, which includes on site weather stations, to control the irrigation at more than 100 schools in the San Diego metropolitan area. This system is projected to save 127 million gallons of water annually, representing a potential cost savings of over $390,000 at current market prices.
Since watering intervals and irrigation amounts are typically dependent upon the type of vegetation or greenery, serious disadvantages may result when operational limitations of an irrigation system are consistently manipulated by manual operational modes without regard to the specific watering needs of particular vegetation.
Evapotranspiration (ET) is a measurement of the total amount of water needed to grow plants and crops. This term comes from the words evaporation (i.e., evaporation of water from the soil) and transpiration (i.e., transpiration of water by plants). Different plants have different water requirements, so they have different ET rates. Plants also have different ET rates at different times in their growth cycle.
Since there are thousands of cultivated plants, experts have tried to simplify matters by establishing a standard ET rate for general reference and use. The standard is referred to as the potential evapotranspiration. This is the potential ET assuming the crop is in a deep soil and under well-watered conditions. The standard crop is a cool season grass which is 4-inches tall. The technical term for this is the xe2x80x9cPotential evapotranspiration of a Grass Reference Cropxe2x80x9d or xe2x80x9cPETxe2x80x9d for short.
PET depends on the climate and varies from location to location. Special weather stations are used to collect the climatic data for calculating PET, including temperature, dew point temperature (relative humidity), wind speed, and solar radiation. A prior art example of a central irrigation and data logging system is the system built and sold by Sensing and Control, Inc. of San Diego, Calif.
The water requirements of specific crops and turf grasses can be calculated as a fraction of the PET. This xe2x80x9cfractionxe2x80x9d is the called the crop coefficient (Kc) or turf coefficient (Tc). Crop coefficients vary depending on the type of plant and its stage of growth. Detailed information on crop and turf coefficients and how to use them is presented at http://agen.tamu.edu/vet/tools/coe-tool.html.
This specification uses PET calculated by the Penman-Monteith method from weather station data. This is one of a number of methods that can be used to determine PET and ET. Several organizations, such as the International Committee on Irrigation and Drainage and the-Water Requirements Committee of the American Society of Civil Engineers have proposed establishing the Penman-Monteith method as a worldwide standard. Such a standard facilitates the sharing of PET data and development of crop coefficients.
In Texas, the Penman-Monteith method is used in the North Plains PET Network, a joint project between the Texas Agricultural Extension Service, the Texas Agricultural Experiment Station and the USDA-ARS Laboratory in Bushland. For more information on the Penman-Monteith equation and other methods for determining PET, see Evapotranspiration and Irrigation Water Requirements, edited by M. E. Jensen, R. D. Burman, and R. G. Allen. Published by the American Society of Civil Engineers, New York, N.Y. 1990. 332pp.
Universities now include irrigation water management within their departments of agricultural engineering. Water management is a critical issue for water conservation districts throughout the country. The cost effective use of irrigation, which is dependant on the proper control of the irrigation system is a major problem for agrobusiness as well as for industry and municipalities. Within large cities, the economical use of water is an absolute necessity, especially use by large users such as school districts, parks and golf courses.
There are significant disadvantages, however, associated with all prior art methods of controlling irrigation systems. For example, all prior art systems define a start time to apply water to the turf or crop. Even if the system has a rain sensor, if the rainfall begins after the system""s start time and the rain quantity is sufficient to supply the necessary water, then all the irrigation water applied prior to the start of the rainfall is wasted. For another example, prior art systems do not maintain a history of soil tension to allow in situ calculation (by least squares, or regression analysis, or any other appropriate method of curve fitting) of a characteristic curve showing the amount of water required to bring the soil moisture (or tension) from its measured value to a desired value. Still another problem associated with all prior art methods of controlling an irrigation system is that prior art systems do not take into account that newly planted landscapes or crops do not have their roots either fully developed or in intimate contact with the soil, thus they may need more water-than would be the case for a mature crop or turf.
In view of the foregoing, it is the primary object of the present invention to provide a method of controlling an irrigation system that is more efficient than the methods taught by the prior art by operating the irrigation system so as to maximize the contribution to the watering event by natural rainfall and by measuring the actual water applied to the crop and the soils actual response to the application of water, thus minimizing the waste of irrigation water.
It is therefore one purpose of the present invention to provide an improved method of controlling an irrigation system wherein the watering event is defined by the stop time of the watering event, rather than by the start time, as taught by the prior art, in order to delay the irrigation as long as is possible in order to allow the system to statistically take advantage of natural rainfall.
Another purpose of the present invention is to provide an adaptive irrigation control that uses data from several recent watering events to determine the actual response of the soil (tension or moisture content) to the application of water.
Still another purpose of the present invention is to provide a method of controlling an irrigation system that modifies the watering schedule based on the predicted probability of rainfall. In this mode, the system would delay or reduce irrigation if the prediction of rain was high and would only irrigate if the predicted rainfall did not occur.
A further purpose of the present invention is to provide an method of controlling an irrigation system having multiple irrigation zones wherein the zone having the greatest water flow rate is irrigated last in order to maximize the possibility of rainfall contribution to the watering event.
Another purpose of the present invention is to provide a method of controlling an irrigation system having multiple irrigation zones that conserves water by irrigating the zone that requires the greatest volume of water last in order to maximize the possibility of the contribution of rainfall to the watering event.
And yet another purpose of the present invention is to provide a method of controlling an irrigation system that measures the amount of rainfall and then calculates the amount of water required to complete the necessary irrigation.
Yet another purpose of the present invention is to provide a method of controlling an irrigation system that provides a xe2x80x98set in modexe2x80x99 to provide the correct amount of water for newly planted crops or turf.
Another purpose of the present invention is to provide a method of controlling an irrigation system that measures the actual amount of water flowing through the system so the irrigation amount can be calculated in inches of water, or other familiar precipitation units.